Patent document 1 discloses the compound represented by the following formula (I), which can be used for improving the heat stability of butadiene polymers. In the incorporation of said compound into butadiene polymers, the compound is generally dissolved into a hydrocarbon solvent, and then mixed into butadiene polymers, as described in Patent document 1.

[Patent document 1] JP-A-1-168643 (Claims, page 6 , the right lower column, lines 8 to 16)